>
>Rich says:
>
>>A proper glitch resistor needs no fuse. My guess is that most of the
>>damage caused by peak fault current (delivered by the filter capacitor)
>>takes place in roughly the first couple of milliseconds.
>
>40swg (0.0048 ins dia) wire fuses at about 2 amps. Suspended between
>suitable supports, it should go in well under 2millisecs, thus reducing the
>energy dissipated in the tube.
? What of the ensuing Cu vapour arc that exists as the wire separates?
Metal-vapour arcs have a v drop of roughly 15v. // A friend of mine
performed an antenna experiment with a eight-foot wooden step ladder and
two poles. He wanted to find out: What is the min. wire gauge that will
safely handle 1500w of AØ on 10m in a half-wave dipole?. He started with
c. 30 ga. Cu and worked down. With 40 gauge Cu wire, the enamel coating
did not get warm enough to discolour.
> Then it has to be replaced, and if the tube
>is a tetrode, some sort of protection is needed for the screen.
? This I doubt. The mass of a typical screen is fairly substantial and
it is typically not gold plated. I had numerous flashovers in the 8171
amp. and there was no screen damage. However, if I screwed up during
tuneup, the fast acting fuse in the primary of the screen supply opened.
> A suitably
>big (physical size/power rating) glitch resistor will presumably hold on
>until the primary breaker comes out, but I just wonder if the strain is
>worth avoiding. At say 3kV, a 50 ohm glitch resistor can be expected to get
>60amps through: that's a fair amount of current for a tube,
? Let's say that oil filled, paralleled, low-ESR filter caps are used
which have a net ESR of 2 ohms. If the supply potential is c. 4kV, I
should expect that the peak fault current would be a bit under 2000A. I
aim for using a glitch R that will keep the peak fault current below
200A.
>capacitor bank. I guess it's case of whether or not the inconvenience of
>changing the fuse
? The sticky wicket seems to be in finding a fuse that will disrupt 2kA
at 4kV, before 2mS, without striking a metal vapour arc. .
- cheers, Peter
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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